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New data from NPD Connected Intelligence shows that Verizon Wireless' (NYSE:VZ) iPhone users are the most prolific data downloaders among the nation's top four wireless carriers. The firm found that the iPhone customers of Verizon used an average of 1.58 GB of cellular data per month in September.

According to NPD's findings, AT&T Mobility (NYSE:T) iPhone users consume an average of 1.35 GB per month, putting the carrier into the No. 2 place. Sprint iPhone users are in the No. 3 position, downloading an average of 0.72 GB per month. T-Mobile USA's iPhone users consume an average of 0.19 GB per month, according to NPD. NPD's figures represent data usage across cellular networks and do not include Wi-Fi data usage. Smartphone customers typically transmit 2 to 3 times more data over Wi-Fi than cellular.

The bulk of AT&T's iPhone users are likely on the carrier's HSPA network. The bulk of Verizon and Sprint's iPhone users are likely on the carriers' CDMA EV-DO networks. And the bulk of T-Mobile's iPhone users are likely on the carrier's EDGE network. (T-Mobile does not sell the iPhone, though the carrier has said that it counts more than 1 million unlocked iPhones on its network. T-Mobile is in the process of launching HSPA services on its 1900 MHz spectrum in order to provide faster speeds to its iPhone customers.)

September is the first month that NPD tracked iPhone data use. Apple (NASDAQ:AAPL) began selling the LTE-capable iPhone late in September. AT&T, Verizon and Sprint are in various stages of building out LTE networks, which provide much faster speeds. Wireless customers typically download more data when they have access to faster networks.

NPD obtained its findings through its SmartMeter software, which is installed on around 110 iPhones (participants are provided "incentives" to install the software on their phones). NPD said it plans to expand that number to 500 by the end of the year. The firm has been tracking Android smartphone data use for months on both cellular and Wi-Fi networks. NPD's findings show that iPhone customers typically use more cellular data than Android smartphone users do.

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